It is known that the antenna required for a radio receiver located in a wristwatch can be embedded in the wristwatch band which holds the watch. One such system is illustrated and described in U.S. Pat. No. 4,713,808 issued to Gaskill et al. and hereby incorporated by reference.
The small size and portable nature of the receiver place stringent demands on the receiver antenna system. For example, the number of stages of RF amplification in the receiver must be kept to a minimum to minimize the drain on its battery. Accordingly, a relatively strong signal must be provided to the receiver from the antenna; however, the small size and portable nature of the receiver dictates that its antenna be small and unobtrusive, thereby producing a relatively weak signal.
In the case of an antenna located in the wristwatch band, additional problems are presented because different users have different physical bodily proportions. One length wristwatch band that can be used by a person with a small wrist will not also be usable by a person with a large wrist. Thus, it is desirable to have a wristwatch band with an adjustable length.
The tuning frequency, f, in an LC electrical circuit, whether series or parallel, is inversely proportional to the product of circuit inductance, L, and capacitance, C, and specifically obeys the following expression: ##EQU1##
Since the inductance of an antenna in a wrist band is proportional to length of the wire, when a wrist band and the associated antenna change in length, the tuning frequency thereof also changes. Thus, by decreasing the length of the antenna watchband for small wrists, inductance also decreases, thereby increasing the tuned frequency of the antenna.